Add versioning for API Gateway defaults

[srchase]

This PR adds versioning to manage API Gateway defaults.

By default, API Gateway conversions will use defaults of version 2023-08-11 which will set the following OpenAPI config options:

• alphanumericOnlyRefs: true
• disabledFeatures: [default]
• disableDefaultValues: true
• disableIntegerFormat: true

All of these can be disabled by setting apiGatewayDefaults to disabled in smithy-build.json:

{
    "version": "1.0",
    "plugins": {
        "openapi": {
            "service": "example.weather#Weather",
            "protocol": "aws.protocols#restJson1",
            "apiGatewayDefaults": "DISABLED"
        }
    }
}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mtdowling]

I think it makes sense to pluralize this